1. Field of the Invention
The present invention relates to an antenna device and a wireless communication device preferably for use in an RFID system that includes a contactless IC card or an RF tag and the like.
2. Description of the Related Art
An RFID system in which a reader-writer and an RFID tag wirelessly communicate with each other in such a manner that information is transmitted between the reader-writer and the RFID tag has been widely used as an item management system. A reader-writer and an RFID tag are each formed of an RFID IC chip for processing a radio signal and an antenna for transmitting and receiving a radio signal, and a predetermined communication is performed between an antenna of a reader-writer and an antenna of an RFID tag via a magnetic field or an electromagnetic field.
In recent years, an RFID system has been introduced in a wireless communication terminal as in, for example, Felica (Registered Trademark), and such a wireless communication terminal may sometimes be used as a reader-writer or an RFID tag. In particular, two antennas, such as a transmission antenna and a reception antenna or an antenna for a tag and an antenna for a reader-writer, capable of being compatible with systems using the same frequency band may sometimes be provided in a wireless communication terminal.
In the case where two antennas capable of being compatible with systems using the same frequency band are provided in one terminal, it is necessary to suppress mutual interference between the antennas. For example, Japanese Unexamined Patent Application Publication No. 2004-213582 and Japanese Unexamined Patent Application Publication No. 2006-126901 disclose configurations in which a conductive member or a soft magnetic member is disposed between two antennas.
On the other hand, for example, in a contactless automatic ticket gate system, during the period when a user is holding an IC card over a reader-writer that is disposed in a main body of a ticket gate, transmission and reception of data is performed between the reader-writer and the IC card. In this case, an antenna of the IC card is held over an antenna of the reader-writer at any of various angles, and reading and writing of the IC card may sometimes not be performed depending on the angle.
Therefore, as disclosed in Japanese Unexamined Patent Application Publication No. 4-134910, Japanese Unexamined Patent Application Publication No. 8-044833, and Japanese Unexamined Patent Application Publication No. 2002-043827, and the like, there is known a reader-writer in which two coil antennas (loop antennas) are disposed in such a manner that the angle formed by coil surfaces (loop surfaces) of the coil antennas is 90 degrees.
According to the antenna devices disclosed in Japanese Unexamined Patent Application Publication No. 2004-213582 and Japanese Unexamined Patent Application Publication No. 2006-126901, although mutual interference between antennas that are adjacent to each other can be suppressed, loss (eddy-current loss) due to a conductive member and a soft magnetic member is likely to be large, and thus, it is difficult to secure a large communication range. In addition, since the configuration of a tag becomes complicated, and also the size of the tag becomes large, manufacturing tolerance is large, and the manufacturing costs are likely to be high.
In the case where one of the antenna devices disclosed in Japanese Unexamined Patent Application Publication No. 4-134910, Japanese Unexamined Patent Application Publication No. 8-044833, and Japanese Unexamined Patent Application Publication No. 2002-043827 is provided in a reader-writer, two coil antennas need to be disposed in such a manner that the angle formed by coil surfaces of the coil antennas is 90 degrees, and thus, the configuration of the antenna device becomes complicated. In addition, the size of the antenna device becomes large, and thus, the installation location and utilization of the antenna device will be limited.